When utilizing Metal Oxide Semiconductor/Field Effect Transistors (MOS-FETs); it is general knowledge that as amplifiers they are limited to small signal situations. It is also known, that when they are structured as depletion type devices, that their ability to amplify incoming signals is not restricted to the reversed biased range of their gate to source voltage handling limitation, but will tolerate temporary excursions into the forward biased range without degrading the impedance between the gate and the source. This characteristic makes possible a zero biased arrangement for the purpose of signal amplification. It is also possible to structure MOS-FETs in a push-pull arrangement so that the above mentioned potential can be maximized.
The fact that the transconductance of such transistors increases in proportion to the on-resistance makes it desirable to structure the channel's cross-sectional dimensions as small as possible. The resect use of lasers in the manufacturing of said devises can reduce such dimensions to much less than one micron, with a high degree of consistency in maintaining such dimensions.
After considering the above mentioned abilities when used in combination, it is realistic to expect a gigantic increase in performance. Said increase would not necessarily manifest itself by virtue of a larger output signal, but more so by the ability of the incoming signal to overcome the internal noise, that is inherent in all electronic amplifiers.
It is the intent of this disclosure to bring to general knowledge an extremely sensitive amplifier arrangement, which can be employed in a wide range of applications.
It is a further intent of this disclosure to bring to general knowledge an extremely sensitive amplifier arrangment, which is not limited in performance by the inherent inaccuracy of biasing resistors.
It is a still further intent of this disclosure to bring to general knowledge an extremely sensitive amplifier arrangement, which is not subject to clipping the incoming signal at the output of the amplifier even though the gates of the transistors may be driven beyond the pinch-off voltage; thus increasing the minimum to maximum signal handling ability.
It is still another intent of this disclosure to bring to general knowledge an extremely sensitive amplifier arrangement, which the generally associated accessories are easily included.
It is, also, an intent of this disclosure to bring to general knowledge an extremely sensitive amplifier arrangement, which the inherent logarithmic characteristics of the transistors of the first amplifying stage are greatly reduced and the variations of the amplification ratio of said stage are reduced by a succeeding amplifying stage.
It is the final intent of this disclosure to bring to general knowledge an extremely sensitive amplifier arrangement, which the generally associated accessories can be included so as to extend their effective range insofar as said accessories can be applied to a radio wave amplifier.
The preceding stated intentions of the present disclosure, which will become apparent upon a reading of the following specification and claims, are accomplished by the opposed positioning of two MOS-FETs (depletion type). These devises, which are connected directly together at their source ends and indirectly together at their drain ends through a center-tapped electromagnetic induction coil or load resistor, represent the essential components of the arrangement. Said electromagnetic induction coil functions as the primary side of a transformer coupling, where as said load resistor requires a capacitor at both ends in order to do the same.
The input to the gates of the opposing transistors can come from the secondary side of a transformer, which indirectly ties the two gates together or from the ends of a microphone diaphragm coil. Said input could, also, come through two separate capacitors. A capacitor is disposed between the gates of the transistors when the secondary side of a transformer coupling is employed for the purpose of accommodating radio frequencies. The need for center-tapping the secondary side the transformers, that conduct incoming signals to the gates, been eliminated.
As it is intended to function as an amplifier, but without the need for biasing resistors the voltage handling ability between the source end of the transistors and their respective input gates is of equal potential into either the forward or reverse voltage range before the impedance between the gate and the channel is burnt out. As the channel's cross-sectional dimensions are intended to be extremely small, the reverse polarity swing of the gate to source would cause the channel's electrical conductivity to cease long before the above mentioned limitation is reached. In order to exploit the full potential of the gate to source voltage handling ability a push-pull configuration is required. The forward polarity swing of the gate to source would be to a point of higher transconductance, which would greatly reduce the clipping effect of the alternate transistor's shift to pinch-off voltage which would be to a point of less transconductance. The extremely small cross-sectional dimensions of the channel are integral with the desire for higher transconductance characteristics.
The supply voltage available to the symmetrical portion of the embodiment may be limited by inserting a variable resistor into the line leading to the point of juncture between the source ends of the two transistors. Said resistance could be either manually or transistorized controlled.
A second optional control may be included by positioning a MOS-FET (enhanced type) between and connected to the two wires leading to the primary side of the transformer preceding the first amplifying stage when said essential components are used for amplifying radio frequencies. The inclusion of such a component will allow the employment of MOS-FETs (depletion type) as amplifiers with an unusually thin layer of silicon dioxide, which acts as an insulator between the gate and the channel. This increases the ability of the incoming signals to overcome the internal noise without fear of burning out the insulating layer due to the extreme strength variations of the incoming signals. Said extreme variations are particularly associated with radar and sonar applications.
In order to maximize the effectiveness of this second optional device the surface area between the two extremes of the voltage induced channel can be enlarged by diffusing said extremes so as to be dispositioned into relatively long parallel lines in close proximity thus reducing the reducing channel's on-resistance. An inclusion of this type of transistor would involve a unique arrangement; in that the source end and the drain end of said component are not established as in all other circuitry, but are continually exchanging polarity at the same rate as the incoming signal. In order for such a relationship to effectively operate neither end of the voltage induced channel can be grounded. Said channel is induced by generating a sufficient voltage of the proper polarity between the gate and the substrate in order to partially and controllably short circuit the primary side of the transformer coupling preceding the first amplifying stage. The inclusion of two biasing resistors are for the purpose of bringing such a device to it's required threshold voltage.
A third option is the matching of depletion type transistors to enhanced type MOS-FETs or enhanced type MOS-Power Transistors. The purpose of directly coupling the two different type of transistors is that as the depletion type are shifted to a point of lesser transconductance the enhanced type would be shifted to a point of greater transconductance. This relationship tends to stabilize the amplification ratio regardless of the variations in the signal strength at the input of the circuit. The possible application of either of the two different types of enhanced transistors would be dependent on the intent for which the curcuit was meant. Enhanced MOS-FETs are strictly for small signals such as radio or radar receiver type, while MOS-Power Transistors are for high power applications such as a transmitter or line driver situation. Those configurations in which the possibility of the first amplifying stage's transistors being driven beyond pinchoff would require the succeeding stage's transistors to have a voltage applied to their gates, that would be well above the transistors threshold point.